Optical pointers such as optical mouse pointers have replaced the conventional rotating ball pointers and become the mainstream. Please refer to FIG. 1 which illustrates the operation of an optical mouse pointer. Principally, a visible light source 10, e.g. a light-emitting diode (LED), disposed in the lower part of the housing 1 illuminates on the plane 14 where the optical mouse rests. The light reflected by the plane 14 and focused by the lens 11. The focused light is transmitted to a photoelectric converter 12, e.g. a charge coupled device (CCD), to be converted into an electric signal. The electric signal corresponding to the image data of the illuminated portion of the plane 14 is then processed by a digital signal processor (DSP) 13 to realize the moving direction and distance of the optical mouse, and a control signal is generated to control the movement of the cursor on the computer display according to the moving direction and distance of the optical mouse on the plane 14. The lens 11, photoelectric converter 12 and digital signal processor 13 are usually integrated as an optical sensor module 15.
In order to achieve the purpose of saving power, the resulting current of the optical sensor module 15 for controlling the visible light source 10 is automatically reduced to lower the illuminance of the visible light source 10 when no movement of the optical mouse is detected for more than a preset period, e.g. a half second. In other words, the optical mouse enters a so-called power-saving state. Since the illuminance of the visible light source is at a low level in the power-saving state, the refreshingly movement of the optical mouse might be neglected particularly when the plane 14 has a less reflective surface or dark color. Therefore, the restore from the power-saving state to the working state might become lagged.
In order to avoid this problem, the illuminance of the visible light source 10 in the working state is raised in a prior art, thereby making the illuminance of the visible light source 10, although reduced in the power-saving state, is still sufficient for detecting the refreshingly movement of the optical mouse. The raised illuminance, however, may be adverse to the stipulation for eye safety. Moreover, the resulting current of the optical sensor module 15 in the suspending mode may exceed the upper limit generally required by a computer system for a general peripheral device.